Become more robust to parse errors

I've started working on a sql [lsp server implementation](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/), using `sqlparser` as the parser. Unfortunately, I very quickly hit a wall, mostly around how `sqlparser` discovers and surfaces errors. For instance, let's say the user types the following: `SELECT * F` and hits the key. A good lsp server would suggest completing `F` to `FROM`, even just do it automatically in that case. If one tries to parse that input string with `sqlparser`, it returns a `ParserError("Expected end of statement, found: F")`. The error isn't unexpected, but now (a) since the ast isn't available in the face of errors, there are no recommendations/commands/lints I can make based on a error-prone AST, and (b) I don't have enough information (line/col info) to send a diagnostic (the thing that makes the red squiggly lines) to the client. The line/col information was suggested in #179, but a fair amount of the work that would enable a really good LSP server implementation is being able to work with an AST that has errors in it.

I _suspect_ what I'm describing is _really_ hard, and has all sorts of backwards-incompatible changes that would be required to make this work. I think it'd be worthwhile, though.

首先阅读 sqlparser 的 ParserError 处理，以及解析 `SELECT * F` 时涉及的 parser 入口点；issue 未提供具体文件或测试。将当前行为与 LSP 诊断要求进行比较，并确定应如何定义容错 AST、completion 支持以及行/列诊断。Done 应包括已达成一致的行为，以及对此示例这类不完整 SQL 的覆盖。

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